We describe the morphological characteristics of two morids, Gadella jordani and Physiculus japonicus, belonging to the order Gadiformes, based on Korean specimens collected from the Korean ocean. Two specimens of Gadella jordani was first collected from Jeju Island, Korea and the East Sea, Korea, in 2013-2014. This species is characterized by 8, 67-69 dorsal fin rays, 66-71 anal fin rays, 5+13 gill rakers, no barbel on the lower jaw, no vomerine teeth, and a ventral luminous organ closer to the anus than to the interventral line. We described it as the first record to the Korean fish fauna, and proposed the new Korean name “Min-su-yeom-dae-gu-sok” for the genus Gadella, and “Min-su-yeom-dae-gu” for the species G. jordani. Physiculus japonicus was first reported by Koh and Moon in the year 1999 based on a single specimen in Korea. However, no study has been attempted to describe the morphological characteristics in Korea since then. In 2013-2014, three specimens of P. japonicus was collected from Jeju Island, Korea and the East Sea, Korea, and we redescribe P. japonicus in detail. This species is characterized by 9-10, 63-64 dorsal fin rays, 70-73 anal fin rays, 3+7-8 gill rakers, a short barbel on the lower jaw, and a ventral luminous organ equidistant between the interventral line and the anus.

The family Moridae in the order Gadiformes comprises 107 species of 18 genera worldwide (Eschmeyer and Fong, 2015). In Japan, 17 species of 8 genera are currently known (Nakabo, 2013), and three species, each belonging to different genera, are found in Korea (Kim, 2011) including Laemonema nana Taki, 1953, Lotella phycis(Temminck and Schlegel, 1846), and Physiculus japonicus(Hilgendorf, 1879). They are distributed worldwide from shallow coastal areas to deep waters (beyond 2,500 m), and less potential value to the fishery except in New Zealand and Australia (Cohen et al., 1990). Fishes of the family Moridae were placed in the family Gadidae until Svetovidov (1948) recognized a distinct family Moridae, based on the uniqueness of the anterior paired projections of the swim bladder connected to the rear of the skull. Among these, four genera (Gadella, Physiculus, Tripterophycis, and Salilota) have a ventral luminous organ (Paulin, 1989; Cohen et al., 1990; Nelson, 2006).

The genus Gadella Lowe, 1843 is differs from other genera by the lack of a barbel on the lower jaw and the diameter and position of the ventral luminous organ (Lowe, 1843; Paulin, 1989). The genus Physiculus Kaup, 1858 is similar to the genus Gadella in some morphological characteristics: ventral luminous organ in advance of the anus, two dorsal fins. But can be distinguished from it by the presence of a barbel on the lower jaw (Paulin, 1989). Recently, two morid specimens were collected by trawl net from the East Sea and Jeju Island in Korea, and were identified as Gadella jordani(Böhlke and Mead, 1951) using both morphological and molecular methods. This species has never officially been included in Korean fish fauna. Here, we describe its detailed morphological characteristics to suggest new Korean names of genus and species.

In Korea, P. japonicus was first reported by Koh et al. (1999) based on a single specimen, thereafter, the morphological characteristics of this species in Korea have not been studied since then. Therefore, we redescribe P. japonicus in detail based on three Korean specimens collected from the East Sea and Jeju Island, Korea in 2013-2014.

Two specimens of G. jordani were collected by bottom trawl from the East Sea and the northeast coast of Jeju Island, Korea. Three specimens of P. japonicus were also collected from the East Sea and Jeju Island, Korea, by trawl and set net in 2013-2014. These specimens were fixed in 10% formalin and preserved in 70% ethanol. Counts and measurements followed Hubbs and Lagler (2004), using a vernier caliper to the nearest 0.1 mm. The vertebrae were counted from a radiograph (Softex HA-100, Japan). The size and position of the ventral luminous organ were measured with the methods of Paulin (1989). These specimens were deposited at the Ichthyology Laboratory at Pukyong National University (PKU), and the Fisheries Resources Laboratory, East Sea Fisheries Research Institute (ESFRI), Korea.

Remarks. The examined specimens were identified as G. jordani based on the lack of a barbel on the lower jaw, no vomerine teeth, and a ventral luminous organ positioned closer to the anus than to the interventral line (Paulin, 1989). Most of the characteristic counts and measurements of the original description (Böhlke and Mead, 1951) correspond well to those of our specimens (Table 1). Böhlke and Mead (1951) placed this species in the genus Physiculus based on the lack of vomerine teeth and the position of the ventral luminous organ. However, Paulin (1989) suggested that this species be placed in the genus Gadella based on the following traits: ciliform teeth on both jaws, ventral luminous organ very small and closer to the anus than to the interventral line, and no barbel on the lower jaw. Three species of the genus Gadella have been recorded in the North Pacific: G. edelmanni(Brauer, 1906), G. jordani(Böhlke & Mead, 1951), and G. molokaiensisPaulin, 1989(Nakabo, 2013). Of these, G. molokaiensis is known only from the Hawaiian Islands (Paulin, 1989; Okamoto et al., 2010). Gadella jordani and G. molokaiensis can be distinguished by snout length in SL (7.0%-7.9% in the former vs. 4.3%-6.6% in the latter), head length in SL (20.8%-24.0% in the former vs. 25.3%-29.1% in the latter), orbit diameter in SL (4.2%-5.1% in the former vs. 5.1%-5.8% in the latter), maxillary length in SL (10.6% -11.9% in the former vs. 12.6%-14.8% in the latter) (Paulin, 1989). However, Sazonov and Shcherbachev (2000) suggested that G. molokaiensis cannot be clearly distinguished from G. jordani and that the two species might be synonymous (Sazonov and Shcherbachev, 2000; Okamoto et al., 2010). Taxonomic characters of two species suggested by Paulin (1989) may be insufficient to identify the two species. Therefore, further studies on morphological and molecular differences of the two species are necessary. Gadella jordani and G. edelmanni can be distinguished by second dorsal fin rays (67-74 in the former vs. 63-65 in the latter), anal fin rays (65-72 in the former vs. 64-68 in the latter), gill rakers (4-5+10-14 in the former vs. 2+10-11 in the latter), diameter of the ventral luminous organ in InV-af (2.5%-4.8% in the former vs. 4.4%-7.0% in the latter) (Paulin, 1989). Except for the genus Gadella, G. jordani is similar to P. japonicus in some morphological characters, including its round head, two dorsal fins, no vomerine teeth, the origin of the 2nd dorsal fin is vertically above the origin of the anal fin, and the ventral light organ is anterior to the anus (Fig. 1) (Paulin, 1989; Koh and Moon, 2003; Okamoto et al., 2010; Nakabo, 2013). However, the two species are clearly distinguished by the presence or absence of a barbel on the lower jaw (absent in the former vs. present in the latter), the diameter of the ventral luminous organ in InV-af (2.5%-4.8% in the former vs. 6.5%-10.6% in the latter), the position of the ventral luminous organ (closer to the anus than to the interventral line in the former vs. generally equidistant between the interventral line and the anus in the latter), and the size of the teeth (equally sized in the former vs. the outer raw teeth are generally larger than the inner teeth in the latter) (Tables 1, 2, Figs. 2, 3) (Paulin, 1989; Koh and Moon, 2003; Yu and Ho, 2012). To identify the species exactly, we compared a 466-base pair mitochondrial DNA COI sequence in Japan G. jordani. The sequences in 2 specimens from this study corresponded well with the sequence in specimen from Japan (genetic distance, d=0.005-0.007) (Fig. 4). Thus, these specimens were identified as G. jordani based on morphological and molecular analyses. We propose a new Korean name “Min-su-yeom-dae-gu-sok” for the genus Gadella and “Minsu-yeom-dae-gu” for G. jordani.

Remarks. As shown in Table 2, the morphological characteristics of these specimens in the present study correspond well with those of the previous studies (Paulin, 1989; Koh and Moon, 2003; Yu and Ho, 2012). In Japan, six species of the genus Physiculus have been recorded: P. japonicusHilgendorf, 1879, P. chigodaranaPaulin, 1989, P. maximowiczi(Herzenstein, 1896), P. nigripinnisOkamura, 1982, P. rhodopinnisOkamura, 1982, and P. yoshidaeOkamura, 1982(Nakabo, 2013). Of these, P. japonicus and P. chigodarana are easily distinguishable by the height of the first dorsal fin (equal to the height of the second dorsal fin in the former vs. higher than the second dorsal fin height in the latter) (Paulin, 1989; Nakabo, 2013). Physiculus japonicus is distinguishable from P. nigripinnis in the number of first dorsal fin rays (9-10 in the former vs. 6-8 in the latter), the color of the dorsal and anal fins (reddish-brown in the former vs. black in the latter); from P. rhodopinnis in the number of first dorsal fin rays (9-10 in the former vs. 6-7 in the latter), the color of the dorsal fins (uniformly reddish-brown in the former vs. lower halves black in the latter); from P. yoshidae in the number of first dorsal fin rays (9-10 in the former vs. 6-7 in the latter), the number of anal fin rays (60-71 in the former vs. 70-77 in the latter), position of the ventral luminous organ (generally midway between the interventral line and the anus in the former vs. closer to the anus than to the interventral line in the latter) (Paulin, 1989; Nakabo, 2013). Physiculus japonicus is most similar to P. maximowiczi in its external shape, but differs in the size of the teeth (outer raw teeth larger than inner in the former vs. equal in the latter), and the presence or absence of gular scales (generally absent in the former vs. present in the latter) (Svetovidov, 1967). However, Cohen (1979) examined the holotypes of P. japonicus and P. maximowiczi and noted that they were quite similar, and suggested that they probably represent the same species. Paulin (1989) later mentioned that P. maximowiczi was a synonym of P. japonicus, but the identification of the two species was not yet confirmed (Eschmeyer, 1998). Therefore, further research is required to resolve the taxonomic confusion of these two species.

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